Printing mediums for ceramic pigments (ceramic mediums) are generally fluids that are used in the preparation of ceramic inks to disperse ceramic pigments, to regulate their viscosity, flowing properties, and binding-cohesive behaviour.
Most traditional ceramic manufactured products, such as wall tiles and floor tiles, are made of a ceramic body that confers form and mechanical properties to the object; the ceramic body generally has some porosity and poor aesthetic qualities.
Said ceramic body, which is defined “green” or, alternatively, “fired”, if previously fired, is then usually coated with ceramic layer, called ceramic glaze; the ceramic glaze is completely sintered by firing, in such a way to gain suitable surface aesthetic qualities and, in the meantime, to become a fluid-proof barrier; as a matter of fact, after firing, the ceramic glaze has usually zero porosity and is generally resistant to abrasion and to the attack of chemical agents such as acids, bases, dyes.
The aesthetic finishing of the ceramic material can be completed by a decoration phase, that is by the application of sinterable and variously coloured ceramic materials (ceramic pigments) which are applied according to a precise drawing (décor).
The decor can be applied either on the green or fired ceramic body, on which the glaze was previously set, or, in the so called third firing decorations, after the firing on the glaze. The main printing techniques used in the decoration either of green or fired ceramic substrate are flat screen printing, rotary screen printing and the decoration by silicone roller (the latter comprising the printing through laser engraved roller, or “rotogravure printing”, and the printing through relief engraved roller, or “silicone stamp printing”); the decoration by silicone roller is also called rotogravure.
All these decoration techniques require a series of overlapping printings, one for each of the colours that compose the drawing. Ceramic inks and printing mediums are formulated according to the kind of ceramic body to which they will be applied (green ceramic, fired ceramic, sintered glaze . . . ) and according to the application technique (brush, spatula, screen printing, rotogravure printing . . . ).
In the preparation of ceramic inks for the screen printing or rotogravure decorations of green or fired ceramic bodies, liquid printing mediums based on mixtures of water and glycols and normally containing additives, such as rheology modifiers, binders and plasticizers, are generally used.
Traditional liquid printing mediums contain large amounts of water, usually about 50% wt of water; their transportation and storing costs are economically and energetically relevant.
Moreover, liquid printing mediums shall be stored in drums or tanks and, because of the variety of slightly different mediums that are normally used in an industrial plant, drums and tanks often need washing cycles with additional spoil of water and heavy duty detergents.
Therefore, it would be advantageous to provide concentrated ceramic mediums in powder form having good versatility.
In the prior art, BR PI0503487 describes a solid ceramic ink which is ready for use after dilution in water and contains frit, binder, thickening agent, antifoam and preserving agent; however BR PI0503487 does not disclose a solid powdery medium.
BR PI92202137 describes a silk print ceramic ink, in the form of paste, that contains a frit and a possibly waterless thixotropic medium, which comprises polyethylene glycol; however, also BR PI92202137 does not disclose a solid powdery medium.
It has now been found that free-flowing mixtures of inorganic absorbent, glycol, urea, and optionally conventional ingredients of ceramic mediums, can be prepared in the form of powder and used as concentrated ceramic mediums.
These concentrated ceramic mediums can be diluted in water and mixed with ceramic pigments to give ceramic inks with proper stability and rheology.
Alternatively, they can be mixed (or milled) with ceramic pigments to give ceramic inks compositions in powder form, which can be diluted in water before use to provide liquid ceramic ink; or, in another embodiment, the they can be milled together with the ceramic pigments and water to give in one step a liquid ceramic ink.
The powdery ceramic mediums of the present disclosure provide ceramic inks that allow the realisation of decors having comparable or improved definition with respect to inks obtained using traditional liquid mediums.